Centrifugal switch



Patented Nov. 29, 1938 UNITED STATES PATENT OFFICE CENTRIFUGAL SWITCH Application January 19, 1935, Serial No. 2,496

11 Claims.

The invention relates to electric switches and more particularly to control devices such as centrifugal switches of the type employed for controlling the speed of electric motors.

When an electric motor is employed to drive a machine that operates at various specific uniform speeds, these speeds may be produced by controlling the speed of the driving motor, but the devices employed heretofore for controlling the speed of such motors have not been entirely satisfactory. For example, the size of such devices has been too large or the life too short for practical application, and therefore, one of the objects of this invention is to provide a control device of the type described that is more compact and at the same time has a longer operating life.

Heretofore, centrifugal switches of this type have not been dynamically balanced with sufficient accuracy to prevent annoying vibration while in use, especially at the higher operating speeds, and unduly rapid deterioration of the motor bearings and switch elements which are subject to this vibration. Therefore, another object is to provide a switch of this type that is dynamically balanced to a high degree so that operation at a relatively high speed will not cause deterioration or injury to either the switch or the motor with which it cooperates.

In prior devices of this kind the centrifugal mechanism has not been sufficiently sensitive to small changes in speed to prevent undesirable fluctuations in the speed of the controlled motor, and therefore another object of this invention is to provide a control device of the type described that will maintain a more nearly constant motor speed. Also, due to manufacturingvariations in the component parts, as well as variations in the characteristics of the materials employed, prior devices have not accurately produced a suitable range of, predetermined speeds. Therefore, another object of this invention is to provide a device of the class described that will more accurately produce a suitable range of predetermined speeds which are clearly marked on the adjusting mechanism.

Prior devices of this kind have also been subject to comparatively rapid deterioration due to wear between the rotating and the stationary cooperating parts, and therefore another object is to provide a device of this type in which the wear between relatively moving parts is reduced to substantially that of the other wearing surfaces of the machine with which it is connected.

In control switches of this type the control contacts often make and break the operating current of the controlled motor at a comparatively rapid rate, and this tends to cause overheating and burning of the contacts which materially shortens their life. Consequently, the contacts in prior devices have been undesirably large in size or undesirably short in life. Therefore, another object is to provide a device of this kind in which the contacts are provided with means for preventing this burning so that they may be small in size and at the same time long in life. Other objects are to provide a device of the type described with an extremely sensitive centrifugal element and means for preventing this element from becoming damaged when rotated at relatively high speed. Another object is to provide such a device with a centrifugal element that may be readily manufactured. A further object is to provide such a device with an adjustable indicating member bearing a scale indicating motor speeds or factors thereof, and means for coordinating these speeds or factors with corresponding motor speeds so that an individually calibrated scale for each device is obviated.

Other objects are to provide such a device that is efficient and accurate in action, long in life, easy and convenient to manipulate, and in which the component parts are interchangeable. These and other objects and novel features will be apparent from the following description and the accompanying illustration, in which:

Fig. 1 is a longitudinal sectional view of a centrifugal switch embodying my invention secured to one end of an electric motor which forms no part of the invention and therefore is not shown in section;

Fig. 2 is a transverse sectional view of the above-mentioned switch taken along line 22 of Fig. 1 showing the structure, arrangement, and support for the electric contacts; and

Fig. 3 is a transverse sectional view of the above-mentioned switch taken along line 3--3 of Fig. 1 showing the connection between the motor and the contacts.

The invention shown by the drawing may be embodied in a centrifugal switch comprising a dynamically balanced centrifugal A that cooperates with an interrupter B which may be moved with respect to the centrifugal by adjustable indicating means 0 to vary the operating point of the interrupter with respect to the speed of the centrifugal.

The centrifugal A may consist of a cylindrical disk or rotor I ll of suitable material such as a metal, of which brass is desirable from the standpoint of the ease with which it may be machined.

For the purpose of attaching the movable elements of the centrifugal the rotor I0 may be provided with diametrically opposed identical slots [2 of which the bottoms slope outwardly from each face of the rotor at a suitable angle. Although the angles may vary according to the type and operating speed of the centrifugal it has been found satisfactory to slope the portion I4 of the bottom adjacent the outer face of the rotor outward at an angle of substantially 30 from the axis of the rotor, and to slope the portion [6 of the bottom adjacent the inner face of the rotor outward at an angle of substantially 60 from the axis of the rotor. Also, although the relative length of the slopes l4 and I6 may vary, a suitable proportion may be obtained when slope i4 is substantially twice the length of slope IS.

The resilient portion of the centrifugal may consist of a bowed spring such as a substantially elliptical spring I8 with its long axis transverse to the axis of rotation and having inturned ends of which each may be provided with a suitable opening by which it may be secured to one of the slopes l6 by means of a suitable fastening such as a drive screw 20. The bowed central portion of spring (8 may be spaced from the outer face of rotor 10, and each end may lie within the outer end of one of the slots l2 a suitable distance from its sloping bottom portion l4 and an equal distance from the axis. To prevent friction between the spring l8 and the rotor ID the width of the spring may be somewhat less than the width of the slots I 2, and to more securely hold the spring l8 in correct alignment and dynamic balance with the rotor the slopes 3 may be suitably grooved to receive the ends of the spring. To operate the spring I 8 the space in each of the slots l2 within each elliptical end of the spring l8 may be provided with a suitable weight 22 that is movably mounted with respect to both the rotor and the spring and fits loosely between the side walls of the slot so that it is free to move outward under the influence of centrifugal force and exert pressure upon the inner surface of spring l8. Although any suitable weights may be employed steel balls such as bearing balls have been found desirable on account of their extreme accuracy in size and weight, and their accurate balance when properly positioned. The relative size of the weights 22 and the strength of spring l8 may vary according to the range of operating speeds and sensitiveness desired, but in the present construction a comparatively high degree of sensitiveness to slight changes in speed has been obtained by employing weights in. in diameter and a spring of steel, such as a clock spring, in. in width and .010 in. in thickness.

In devices of this kind a centrifugal that is sensitive to slight changes in normal operating speeds may be injured at higher speeds. In the present construction however, this contingency is obviated by providing the centrifugal with a buffer spring 24 that limits the travel or deformation of spring [8 and prevents such injury. This spring 24 may be a helical spring located between the rotor I 0 and spring l8 and one end may be secured in an annular groove 26 in the outer face of rotor I0 by suitable means such as frictional engagement with the walls thereof, and the other end may be provided with an abutment member 28 frictionally secured to the spring and having an outer face spaced a short distance from the inner face of spring I 8 when this spring is not deformed by centrifugal force.

As the purpose of this centrifugal switch is to control the speed of an electric motor it may be secured directly to one end of the motor with which it cooperates. To this end the rotor 10 may be provided with an axial opening 30 at the center of weight and of suitable size to properly fit upon the projecting outer end of a shaft 32 of an appropriate motor 34. The rotor l0 may be secured in this position on shaft 32 by appropriate conventional means such as a set screw 36. When only one set screw is employed, and this screw does not entirely fill the opening in the rotor in which it is located, an opening may be provided in the opposite side of the rotor substantially the same size as the unfilled portion of the opening in which the set screw is located in order to more easily preserve the accurate balance of the rotor.

The centrifugal A may be inclosed in a suitable casing 38 which for convenience may be in the form of a hollow cylinder provided with a suitable number of inturned ears 40 by which it may be secured to the end of motor 34 by suitable conventional fastening such as a plurality of screws 42. The inner cylindrical wall of casing 38 may be spaced from the centrifugal a suitable distance to allow for expansion of spring I8 and also for conductors connecting the switch with the motor. Also, the casing may be of suitable length to provide space for the interrupter.

The interrupter B may consist of a pair of suitable contacts 44 and 46' respectively secured to appropriate springs 48 and 50 that are secured to a dielectric terminal block 52 by conventional means such as bolts 54. This terminal block may be secured to casing 28 by suitable hinges or pivots such as a pair of resilient conductors 56 and 58 each having an overturned end secured to the terminal block by one of the bolts 54 and an overturned end adjacent the end of motor 34 to which a suitable conductive wire may be secured. These conductors 56 and 58 may be secured to the inner surface of casing 36 by an overlying clamping member 60 which in turn may be secured to the casing by a suitable fastening such as one or more screws 62, and.- these conductors may also be insulated from the casing by suitable dielectric material such as an appropriate length of varnished insulating tubing 64 in which they may be inclosed.

For the purpose of securing proper cooperative relation between the contacts 44 and 46, one of the contact springs, such as 48, may be secured to the side of contact block 52 facing the centrifugal A, and the other spring, such as 50, may be secured to the side opposite the centrifugal. Also, to secure suitable cooperative relation between the centrifugal and the interrupter, spring 48 may cross the axis of the centrifugal and this spring may be provided with a suitable mechanical contact bearing button or thrust button 66, of appropriate wear resisting dielectric material such as fiber located in alignment with the axis of the centrifugal. During operation the rotating spring I 8 bears upon the thrust button 66 with sufficient pressure to operate the contacts, and the wear between these relatively moving parts may be reduced to a negligible minimum by providing this thrust button with an insert 68 of suitable lubricating material such as graphite or the like.

Also, during operation, the contacts 44 and 46 may interrupt the operating current of motor 34 at a relatively rapid rate, and this continuous interruption tends to generate considerable heat at the contacts which, if not dissipated, may cause relatively rapid deterioration. In the present construction, however, the heat generated atthese contacts may be dissipated or radiated by providing heat conducting members, such as washers 70, in heat exchange relation with the contacts. These heat radiating members may be of metal having a high conductivity of heat, such as copper, and they may be of somewhat larger size than the contacts or contact supporting springs.

For convenience in mounting these washers may be secured to the contact springson the side opposite the contacts by providing the contacts with supporting shanks or stems of sufficient length to extend through a supporting spring and one of the heat dissipating members where the end of the shank may be upset, overturned, or riveted to secure the assembly together.

The outer end of casing 38 may be closed by suitable means such as adjustable indicating means composed of a cap 12 which may be movably mounted on the casing by appropriate coacting formations such as interfitting threads 14 on the outer surface of the casing and the inner surface of the cap, and suitable operating connection may be provided between this cap 12 and the interrupter B so that the position of the interrupter with respect to that of the centrifugal may be changed by movement of this cap to vary the operating point of the interrupter with respect to the speed of the centrifugal and thereby vary the speed of the controlled motor.

For this purpose the cap 72 may be provided with an adjusting plate 16 in operative relation with a cooperating adjusting button 18 which may be carried by a relatively rigid contact adjusting arm 80 rigidly secured to terminal block 52 by a conventional fastening such as screw 82. The relative position of cap 12 with respect to casing 38 may be indicated by a scale graduated in rotative speeds of motor 34 or some factor dependent upon the speed of the motor. This scale may be carried by either the cap or the easing, but for convenience of manufacture a separate scale 84 may be provided which extends substantially around the periphery of cap 12. For purpose of appearance this scale may be embedded in an appropriate circumferential groove in the outer surface of the cap 12, to which it may be secured by suitable fastening such as one or more rivets, pins, or drive screws 86. As the entire range of motor speeds desired may be secured by one revolution of cap 12, it may be limited to this range of movement by providing the cap and easing with suitable stops such as a lug 88 extending outward from the end of casing 38, and a cooperating screw 90 extending inward from the inner surface of cap 12.

In order to adjust the speed of motor 34 to some particular speed factor, for example, the lowest shown by scale 84, means may be provided for adjusting the operating point of the interrupter with respect to the speed of the motor by varying the position of plate 16 with respect to that of cap 12. This may be accomplished by providing plate 16 with a threaded stem or shank 92 that extends outwardly through a correspondingly threaded opening in cap 12 at a suitable point such as the axis where it may be secured against inadvertent movement by a lock nut 94. In addition to this adjustment, means may be provided for varying the ratio of movement between the cap and the interrupter to secure proper coincidence between the other speed factors shown by scale 84 and corresponding motor speeds. This may be accomplished by providing means for adjusting the distance of adjusting button 78 from the fulcrum around which the interrupter moves. To secure this adjustment, adjusting arm 80 may be provided with a series of openings 96 at various distances from the resilient ends of conductors 56 and 58, which form a fulcrum for the interrupter, and adjusting button '18 may be secured in any one of these openings found necessary to secure the degree of coincidence desired.

For purpose of operation the contacts of the centrifugal switch may be connected in series with the electric circuit of the motor, and this may be conveniently accomplished by connecting one of the motor conductors, such as 98, with one of the switch conductors, such as 56, and then providing the other switch conductor, such as 58, with an electric conductor or wire such as I that extends to the outside of the switch casing where this conductor together with the other motor conductor I02 may be conveniently connected with a supply circuit.

These connections may be made by bringing the motor conductor 98 into the switch casing through a suitable opening and then connecting this conductor, by suitable means such as solder, with the overturned inner end of switch conductor 56. Conductor I 00 may also be brought into the switch casing through the same or a similar appropriate opening and then connected with the inner overturned end of switch conductor 58 by similar suitable means.

Although the weights 22 are not rigidly secured to the rotor I0 they are held diametrically opposite each other by the slots I 2. When the rotor is rotating these weights lie against the inside of the outer ends of spring l8 which are equal distances from the axis of the rotor, and this, together with the fact that the weights are exactly alike, produces a centrifugal that is dynamically balanced and imparts no appreciable vibration to the motor or the switch. Furthermore, for the reason that the spring I 8 is secured to the rotor at a point closely adjacent each of the portions that control the position of the weights, any deformation of the spring during operation does not move the weights out of dynamic balance even at relatively high operating speeds, and any tendency toward such movement is restricted to such an extent that it is not appreciable by the fact that the spring I8 is of such a form that the weights move a relatively small amount in proportion to the axial or operating portion, and by the fact that the movement of this portion of the spring is limited by the buffer 24 to that necessary to operate the contacts.

During the operation of the apparatus just described, the centrifugal force of the revolving weights 22 expands the looped spring l8 and draws the central portion at the axis of the rotor in a direction away from the interrupter various distances according to the speed of rotation. When springs 48 and 50 are in free condition contacts 44 and 46 are separated a sufficient distance to break the motor circuit, although when the motor is idle or rotating at a speed below that indicated by the scale 84 the contacts are held together by the pressure of spring l8 upon the button 66 carried by contact spring 48. Thus, when the motor speed increases to that indicated by the scale 84 the closing pressure of spring i8 is withdrawn from the contacts 44 and 46 and they are separated by the resiliency of their supporting springs 48 and 50 thereby opening the motor circuit. Therefore, the speed of the motor is maintained at substantially that indicated by the scale.

Due to the more or less elliptical shape of spring l8, the central portion which operates the contacts moves a relatively large amount in proportion to changes in speed of rotation, and this movement is imparted to the contact supporting springs at a point much nearer the fulcrum than the contacts, the contacts are moved a relatively large amount in proportion to the movement of spring l8, and therefore this centrifugal switch maintains the motor at a more constant and accurate speed than devices of this kind known heretofore in which the centrifugal was less sensitive and the operating contacts moved at the speed of the controlling portion of the centrifugal. Also, as the entire contact assembly or interrupter is moved as a unit with respect to the centrifugal by movement of the speed adjusting member, the contact separation remains constant and the resistance of contact spring 48 to the contact closing pressure of the centrifugal remains constant and uniform throughout the range of adjustment and this tends to further increase the sensitivity of the switch and its accuracy of operation.

When prior devices of this kind are adjusted to a relatively high speed and the motor is idle or operating at a speed below the setting of the adjustment, the centrifugal exerts a relatively high degree of pressure upon the bearing surface between the rotating centrifugal and the stationary contacts as well as upon the contacts and their supporting structure. This tends to cause rapid Wear upon the bearing surface and undue deterioration of the contacts and their supports In the present structure, however, these undesirable conditions are obviated by mounting both contact supporting springs 48 and 50 so that they are free to fiex in response to closing pressure or movement greater than that required to flex one spring and close the contacts, and therefore the bearing pressure between the centrifugal and the contacts is sufficiently low to prevent undue wear and rapid deterioration, and the pressure upon the contacts and their supporting springs is not high enough to cause injury or changes in adjustment or operation.

The scale 84 may be graduated to directly indicate the speed of the controlled motor or any factor or result dependent upon the motor speed. Also, the form, shape, and relative position of the component parts may be different from that shown, and other suitable materials and conventional or well known elements may be substituted for those described without departing from the scope of the invention or the advantages derived therefrom.

I claim:

1. A centrifugal switch comprising a centrifugal adapted to be rotated; a pair of cooperating electric contacts in operative relation with said centrifugal and in series with an electric circuit; a pivot for supporting said contacts; and means for moving said contacts around said pivot to vary the distance between said contacts and said centrifugal and thereby control their cooperating influence.

2. A centrifugal motor speed governor comprising a casing; a centrifugal within said casing adapted to be rotated by a motor; a pair of cooperating contacts within said casing in operative relation with said centrifugal and suitably connected in series with the operating circuit of said motor; an adjusting member movably mounted upon said casing for varying the relative position of said contacts with respect to said centrifugal for varying the speed of said motor; a scale in operative relation with said adjusting member for indicating the speed of said motor; and means movably mounted on said adjusting member for initially varying the contact pressure of said contacts to secure coincidence between the speed of said motor and that indicated by said scale.

3. A centrifugal motor speed governor comprising a casing; a centrifugal within said casing adapted to be rotated by a motor; a pair of cooperating contacts within said casing in operative relation with said centrifugal and suitably connected in series with the operating circuit of said motor; an adjusting member movably mounted upon said casing for varying the relative position of said contacts with respect to said centrifugal for varying the speed of said motor; a scale in operative relation with said adjusting member for indicating the speed of said motor; and means for varying the ratio of movement between said adjusting member and said contacts to secure coincidence between the speed of said motor and that indicated by said scale throughout the range thereof.

4. A centrifugal switch comprising a casing; a

centrifugal within said casing; a pair of cooperating contacts within said casing in operative relation with said centrifugal; an adjusting member rotatably mounted with respect to said casing for varying the relative position of said contacts with respect to said centrifugal to vary the operating point of said contacts with respect to the speed of said centrifugal; and cooperating means on said casing and on said adjusting member for limiting the movement of said adjusting member to substantially one revolution.

5. A centrifugal switch comprising a. rotor; a substantially elliptical spring operably secured to said rotor; a suitable weight in operative movable relation with the inner surface of each elliptical end of said spring; and a pair of electrical contacts in operative relation with said spring.

6. A centrifugal switch comprising a rotor; a substantially elliptical spring operably secured to said rotor with its long axis transverse to the axis of said rotor; a suitable weight in relatively movable relation with the inner surface of each elliptical end of said spring; and a pair of electrical contacts in operative relation with said spring.

7. A centrifugal switch comprising a rotor; a substantially elliptical spring operably secured to said rotor; a weight movable with respect to said spring and said rotor in operative relation with the inner surface of each elliptical end of said spring; and a pair of electrical contacts in operative relation with said spring.

8. A centrifugal switch comprising a centrifugal composed of a cylindrical rotor provided with diametrically opposed slots in the outer portion thereof; a substantially elliptical spring having one end thereof secured in and substantially closing the outer end of each of said slots; a pair of cooperating electric contacts operatively associated with said elliptical springs; and a bearing ball movably mounted in each of said slots in operative relation with the inner surface of said spring.

9. A centrifugal switch comprising a. centrifugal composed ofa rotor; a pair of weights rotatable with said rotor; a spring secured to said rotor in operative relation with said weights so that said spring may be deformed by the centrifugal force exerted by said weights; a pair of cooperating electric contacts operatively associ- 5 ated with said springs; and a buifer spring secured to said rotor to limit the deformation of said first mentioned spring.

10. In a centrifugal switch, the combination or a rotary element adapted to be deformed a 10' varying amount according to the speed of rotation; a circuit interrupter operable by the deformation of said rotary element for controlling the speed thereof and movable with respect to said rotary element to vary the speed thereof:

15 adjustable indicating means movable with said interrupter for varying the speed of said rotary element by varying the relative position of said,

interrupter with respect to said rotary element; and means for varying the ratio of movement 20 between said interrupter and said indicating means for securing coincidence between the speed of said rotary element and those indicated by said indicating means throughout the range of speeds indicated thereby.

11. In a centrifugal switch, the combination of a rotary element adapted to deform a varying amount according to the speed of rotation; a circuit interrupter operable by the deformation of said rotary element for controlling the speed 5 thereof and movable with respect to said rotary element to vary the speed thereof; adjustable indicating means movable with said interrupter for varying the speed of said rotary element by varying the relative position of said interrupter 10 with respect to said rotary element; means for varying the relative position of said interrupter with respect to said indicating means for securing coincidence between the speed of said r0- tary element and a particular speed indicated by 15 said indicating means; and means for varying the ratio of movement between said interrupter and said indicating means for securing coincidence between the, speed of said rotary element and those indicated by said indicating .0 means throughout the range of speeds indicated thereby.

LLOYD W. YOUNG. 

